They don't define a KiCad string class, so the header file name was
somewhat misleading. But the fact that they didn't match definitely
made coding more difficult.
The editor has an entry to set a comment associated to a graphic item.
It is only for the designer, but the code to save it in .wks file when not empty was missing.
The code to read it exists since the beginning, so no change in file format
Keeping them in base_units means that we can't introduce
any dependence on these functions to anything that needs to
compile without one of the unit defines (EESCHEMA, PCBNEW, etc)